Heavy duty delta connection



H. H. RUDD Sept. 29, 1942.

Filed June 12, 1941 2 Sheets-Sheet l- Sept. 29, 1942.

H. H. RUDD HEAVY DUTY DELTA CONNECTION Filed June 12, 1941 2Sheets-Sheet 2 MMQM,

,HU l l l r V 1 1 1 H LH WN I Patented Sept. 29, 1942 HEAVY DUTY DELTACONNECTION Harold H. Rudd, Greensburg, Pa., assignor to Railway andIndustrial Engineering Company, Greensburg, Pa., a corporation ofDelaware Application June 12, 1941, Serial No. 397,822

12 Claims.

This invention relates to heavy duty delta connections, and particularlyto delta connections for use between an electric furnace and atransformer having for each phase a plurality of secondary windings withindividual terminal members.

The bus or delta connections for supplying a low voltage, heavy currentto a Heroult furnace comprise a plurality of copper bars of rectangularcross-section that should be vertically arranged to present a minimumsurface area upon which dirt may collect. The current flow may be of theorder of thousands of amperes, for example 40,000 amperes and upwards,and it is therefore desirable to reduce the inductance to a minimum byinterlacing the conductors, by making the connections of all phases ofapproximately the same length, and by reducing the length of allconductors to a minimum. It has not been possible to satisfy theseapparently contrary design requirements with the previously proposeddelta connections from three phase transformers with multiple sectionsecondary windings, and the interlacing of conductors of approximatelythe same length for each phase resulted in relatively long busconductors that extended to a considerable distance above and/or belowthe level of the horizontally arranged bus members that were connectedto the transformer terminals of the secondary windings.

Objects of the present invention are to provide delta connections or busmembers of relatively short length and space requirements that areinterlaced to reduce the inductance of the connections to a minimum. Anobject is to provide delta connections comprising vertically disposedbar conductors located at only two levels above and/or below the levelof the horizontally alined bar conductors that are secured to theterminals of multiple section secondary windings of a transformer. Afurther object is to provide delta connections for multiple sectiontransformer secondary windings in which the connecting members of eachset are of the same length and, if desired, the connecting members ofall sets may have the same length.

These and other objects and advantages of the invention will be apparentfrom the following specification when taken with the accompanyingdrawings in which:

Fig. 1 is a schematic perspective view of a bus system or heavy dutydelta connection embodying the invention;

Fig. 2 is a fragmentary side elevation of the bus system;

Fig. 3 is a fragmentary plan View of the same;

Fig. 4 is an enlarged and fragmentary vertical section of the bus systemas seen on the plane indicated by the line 44 of Fig. 2;

Fig. 5 is a vertical section through one set of interphase connectingmembers as seen on the plane of line 5-5 of Fig. 3;

Fig. 6 is an enlarged fragmentary vertical section as seen on the planeof line 6-45 of Fig. 3;

Fig. '7 is an enlarged and fragmentary perspective view of connectingmembers that extend between bus bars of the outer windings of the threephase transformer; and

Fig. 8 is a similar enlarged fragmentary perspective view of connectingmembers that join bus bars of an adjacent pair of transformer windings.

In Fig. 1 of the drawings, the reference characters T identify generallythe conventional stepdown transformers, with multiple section secondarywindings, of the individual phases A, B, C of the supply system for aHeroult electric furnace. For convenience of description, the polaritiesof the secondary winding terminals at a given instant are indicated byand signs and the associated bus bars will be referred to as of positiveand negative polarity. The secondary winding terminals alternate inpolarity in each phase and the relative arrangement of the polaritiesmay be the same in all phases, as illustrated, or may be reversed in oneof the phases.

The secondary windings of each phase are to be connected in parallel,and delta connections to the three electrodes or groups of electrodes ofthe Heroult furnace call for the connection of the terminals of onephase to the terminals of the adjacent phase. As indicated at the leftof Fig. 1, the delta supply system is established by connecting theterminals of the C phase secondaries to the terminals of the A phase,connecting the terminals of the A phase to the terminals of the B phase,and connecting the terminals of the B phase to the terminals of the Cphase.

A bus bar, or preferably a pair of bus bars, extends horizontally fromeach secondary winding terminal, and the bus bars of opposite polarityare of different lengths. As illustrated in Fig. 1, short bus bars la,lb, lc are connected to the terminals of the secondary windings ofphases A, B and C, respectively, and longer bus bars 2a, 2b, 2c areconnected to the corresponding terminals of the several phases. Thesebus bars are alined horizontally and with their larger surfaces arrangedvertically. Inverted L-shaped plates 3a of the A phase is connected to along horizontal arm of the correspondingly arranged plate 30 of the Cphase. 7

Bars or risers 5a, 50 extend upwardly from the conductors Ia, Ib of theA and B phases, re-.

spectively, and similar bars 6b, 60 extend upwardly from the conductors2b, 2c of the B and C phases. These sets of vertically arranged barsextend above the level of the cross bars 4 of the +AC phase connectionsand are connected by the diagonally arranged sets of parallel bars I, 8of the AB+ and BC+ connections, respectively. All of the connecting barsof each set are of the same length, and the bars I that join the riserbars 5a, 61) have the same length as the bars 8 that join riser bars 5band 60 when, as is customary, the B-phase bars lb, 212 are centrallylocated between the main bus bars of the other phases.

An appropriate physical construction for establishing the schematicallyillustrated circuit connections of Fig. 1 is shown in Figs. 2 to 8,inclusive. The transformer windings are housed in an oil filledtransformer casing T that is spaced from the furnace room by a wall W.The

bar terminals 9 of all transformer secondary windings extend the samedistance above the casing T to receive the horizontally alined sets ofmain bus bars. All sets of bus bars are connected to the transformerterminals 9 in the same manner but only the connections for the C-phasebars and 2c are illustrated in Figs. 2 and 3. A bus bar is arranged ateach face of each terminal bar 9, and is secured to the terminal by theplates ID that are drawn towards each other by bolts II, withininsulating sleeves I2, to compress the assembly of conducting membersand insulating spacers l3, I3 that are located between the adjacent busbars and between the clamping plates Ill and the outer bus bars,respectively. The insulating spacers extend beyond the overlappedportions of the terminals and bus bars, and are notched at their cornersto receive the clamping bolts.

The sets of bus bars la, 20, etc. extend through and are supported by aninsulator I4 that is mounted in the wall W, and the longer positivepolarity bars 2a, 2b, 2c are additionally supported by notched insulatorstrips I that are bolted together and carried by brackets I6 fixed tothe furnace room side of the partition wall'W.

The vertical risers of the interphase cross-connections are preferablyeach individually bolted between the associated pair of bus bars, asshown in Fig. 4 with respect to the riser bars or plates 30, to permitthe replacement or repair of any one cross-connection without disturbingthe other interphase connections. The plate and associated bus bars I-chave alined openings to receive the short stud bolts I! that arethreaded into a sleeve or bushing I8. The stud bolts may be backed outof the sleeve in the narrow space between the bars I, I0 and the adjacent bus bars 20 of opposite polarity.

As shown in Figs. 2, 3 and 4, the sets of crossconnecting bars arerigidly supported in spaced parallel relation by clamps comprisingnotched strips I9 of insulating material and bolts 20.

The electrical and mechanical connections between the several cross barsand the associated riser bars or plates are preferably established bymilling grooves 2| in the riser members, and sweating or brazing thecross connecting bars into the grooves, Figs. '7 and 8.

The connections from the bus system to the furnace electrodes may be ofany desired flexible type but the connections are preferably establishedat the points where cross-connections are made to the main bus bars. Asshown in Figs. 2 and 3, the furnace leads 22 terminate in yokes 23 thatextend over the several pairs of bus members'Za, 2b and 2c, and areclamped to the same by the bolts 24 that extend through the bus membersand the associated riser members 3a, 6b and 6c.'

Attention is directed to the fact that all of the fiat bus andconnecting bars are vertically arranged to present minimum area surfacesupon which dust or dirt may collect, and that the cross-connections arearranged at only two levels above or below the main bus conductors. Theinterlacing of the positive and negative leads is maintained throughoutsubstantially the length of the bus system to reduce induction to aminimum, the length of the connecting members in each phase is the same,and the lengths of all connecting members are or may be identical. Asdistinguished from prior three level delta connection systems such asthat shown in Nye 1,370,989, the bus bars are interleaved, and theconnecting members are all vertically arranged and of the same length.Attempts have been made to improve the mechanical and electricalcharacteristics of the prior delta connections for electric furnaces butthe prior designs materially increased the total amount of copper andthe space requirements. One prior proposal called for an assembly of busand connecting members at five horizontally alined levels or stages, thelength of the assembly as measured from the partition wall to thefurnace leads was over 20% above the corresponding dimensions of a bussystem embodying this invention, and the overall height of the priorsystem was more than the overall height requirement for a three leveldelta connection system according to this invention. Ample space isusually available in a furnace room for any bus system but the pertinentfact is that the total amount of copper is materially increased when theoverall volume of the bus system is increased by'some 240%.

The embodiment herein shown and described is typical f the invention butit is to be understood that changes may be made in the several parts,and their relative size, shape and arrangements Without departing fromthe spirit of my invention as set forth in the following claims.

-I claim:

1. In a bus system for establishing delta output connections for athree-phase transformer having for each phase multiple section secondarywindings withtransversely alined and interleaved positive and negativeterminals, sets of horizontally alined bus bars with alined end portionsto be secured to the terminals of the windings of the several phases,and connecting members joining the bus bars of opposite polarityofadjacen't phases; said connecting members including horizontallyalined connecting bars spaced vertically from said bus bars, :andtheconnecting bars between adjacent sets of bus bars being spaced fromsaid bus bars by a greater distance than that between the bus bars andthe connecting bars that extend between the outer sets of bus bars.

2. In a bus system, the invention as claimed in claim 1, wherein all busbars that are to be connected to transformer terminals of the samepolarity are of equal length and the bus bars that are to be connectedto transformer terminals of opposite polarity are of unequal length, theconnecting bars between the outer sets of bus bars extendingtransversely of the bus bar assembly, and the connecting bars betweenadjacent sets of bus bars being parallel and inclined to the sets of busbars.

3. In a bus system for establishing delta connections to a three-phasepower source having for each phase a plurality of alternately arrangedterminals of opposite polarities, sets of interleaved bus bars havingtransversely alined portions to be connected to the opposite polarityterminals of the several phases, vertically arranged members secured tothe bus bars, and connecting members extending between the verticallyarranged members of opposite polarity of adjacent phases, the totallengths of the vertically arranged members and associated connectingmembers of each interphase connection being substantially identical.

4. In a bus system for establishing delta connections to a three-phasepower source having for each phase a plurality of alternately arrangedterminals of opposite polarities, sets of interleaved bus bars havingtransversely alined portions to be connected to the opposite polarityterminals of the several phases, vertically arranged members secured tothe bus bars, and connecting members extending between the Verticallyarranged members of opposite polarity of adjacent phases, the totallengths of the vertically arranged members and associated connectingmembers of all interphase connections being substantially identical.

5. In a heavy duty delta connection system for use between an electricfurnace and a threephase transformer having in each phase a plurality ofsecondary windings, a plurality of sets of vertically arranged andhorizontally spaced bus bars of rectangular cross-section to beconnected to the transformer secondary windings of the respectivephases, all bus bars of the same polarity being of the same length andthe bus bars of opposite polarities being of different lengths, platessecured to and extending vertically from the opposite polarity bars ofthe outer sets of bus bars, connecting members joining thecorrespondingly arranged pairs of plates, bars extending vertically fromthe other bus bars and of greater height than said plates, and sets ofconnecting bars joining the correspondingly arranged verticallyextending bars of opposite polarity of adjacent phases.

6. In a heavy duty delta connection, the invention as recited in claim5, wherein said plates are of L-shape, and the connecting membersjoining said plates are of the same length and extend transverselyacross the bus bar assembly.

7. In a heavy duty delta connection, the invention as set forth in claim5, wherein said connecting bars are parallel and all of the same length,said connecting bars extending across said bus bar assembly at asubstantial angle to said bus bars.

8. In a heavy duty delta connection, the invention as claimed in claim5, wherein said vertically extending bars have a height substantiallygreater than said plates, and the length of all vertically extendingbars and associated connecting bars is substantially equal to the heightof said plates plus the length of the connecting members joining thesaid plates.

9. In a heavy duty delta connection, the invention as claimed in claim5, wherein said vertically extending bars are all of the same height andthe connecting members joining said vertically extending bars are all ofequal length and horizontally alined.

10. In a heavy duty delta connection, the invention as claimed in claim5, wherein said vertically extending bars are all of the same height andthe connecting members joining said vertically extending bars are all ofequal length, horizontally alined and spaced vertically from the busbars and the connecting members joining said plates.

11. In a heavy duty delta connection, the combination with a pluralityof interleaved and horizontally alined bus bars of opposite polaritiesfor each phase of a three-phase supply system, one set of the ends ofsaid bus bars being transversely alined for connection to current-supplyterminals, the other ends of the bus bars of one polarity beingtransversely alined and constituting current-output terminals and theother ends of the remaining bus bars terminating short of saidcurrent-output terminals, and means including connecting barshorizontally alined at two levels connecting the opposite polarity busbars of adjacent phases.

12. In a heavy duty delta connection for a transformer having multiplesection secondary windings for each phase, bus bars having transverselyalined ends for connection to the secondary winding terminals, membersextending vertically from said bus bars, said members having groovesformed therein, and connecting members seated in said grooves andextending between the vertically extending members of opposite polarityof adjacent phases.

HAROLD H. RUDD.

